Go here to get the Firefox Backup Extension:
http://customsoftwareconsult.com/extensions/febe/febe.html

you might want to do a backup of your current profile with Febe.

THEN go here and get Profile switcher:

https://nic-nac-project.org/~kaosmos/profileswitcher-en.html


Then simply create multiple profiles, and switch between them or open mutiple, and have a gmail account for each profile. Then switch between them. You can have multiple profiles open at once with this tool. One profile doesn't know what the other is doing so you can have multiple gmails, yahoos, etc open at one. Just create a profile for it.
You can also label them in the lower right corner, from within preferences.(once installed, go to addons, and set the preferences for profile switcher.)
If you develop apps have a developing profile, or have one profile with many many many many extensions, and then a profile that's more lean.

With Febe you can back up all your extensions into one file and then
open it in the new profiles and viola! you have all the extensions from your default profile if you want it, or you can selectively install extensions from a full backup. Your choice!


Enjoy.